KVM: nVMX: Don't reread VMCS-agnostic state when switching VMCS

When switching between vmcs01 and vmcs02, there is no need to update
state tracking for values that aren't tied to any particular VMCS as
the per-vCPU values are already up-to-date (vmx_switch_vmcs() can only
be called when the vCPU is loaded).

Avoiding the update eliminates a RDMSR, and potentially a RDPKRU and
posted-interrupt update (cmpxchg64() and more).

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>